Kinetic studies on soybean LOX-3 and curcumin have shown a non-competitive mechanism of inhibition. Curcumin undergoes a photochemical reaction in the X-ray beam when trapped within LOX. LOX-3 becomes complexed with the X-ray induced oxidation and degradation product. Curcumin undergoes photolysis in the laser beam and it has been found that its cytoxicity is greatly enhanced by light. The photoproduct of curcumin binds as a peroxide in the central cavity of lipoxygenase in an Enz-Fe—O—O—R fashion facilitating the inhibition of LOX-3. Combinations of curcumin and retinoic acid have been to shown to have a particularly potent inhibitory effect on the proliferation of human promyelocyte leukemia HL-60 cells.